Study On Wave Flow Field Of Proton Exchange Membrane Fuel Cell

At present,a series of serious problems such as the world energy crisis and global warming are profoundly affecting the sustainable development of society.Traditional fuels have the disadvantages of non-renewability and strong environmental damage of combustion products.Energy structure transformation and new energy substitution have become important issues to be solved urgently in social development.Compared with other energy sources such as petroleum,wind energy and biomass energy,hydrogen energy has significant advantages.Various equipment and devices with hydrogen energy as the main energy source have also received extensive attention.Proton exchange membrane fuel cell(PEMFC)is one of the effective carriers of hydrogen energy,and its application as a power battery in the automotive field is gradually increasing.Different from the energy storage battery,PEMFC is an energy conversion device that converts the internal chemical energy of hydrogen and oxygen into electrical energy.Because liquid water is its single product,it can achieve the ideal index of zero pollution to a certain extent.Bipolar plate is an important part of proton exchange membrane fuel cell.The flow field structure inside the bipolar plate can induce the diffusion of reactants in the gas channel,so that the gas can fill the whole flow field reasonably.As the initial position of the reactant in the battery and the only channel for the discharge of the product water,the design and development of the flow field is very important.This thesis provides a reference for the structural design and performance research of the new flow channel of proton exchange membrane fuel cell wave plate,especially for the related research of serpentine flow channel.In this thesis,a four serpentine-wave flow field structure of PEMFC is constructed,and the multi-physical field simulation analysis of the flow field is carried out by using the computational fluid dynamics simulation software COMSOL Multiphysics.The mathematical model,boundary conditions,geometric parameters and operating parameters of the numerical simulation are analyzed and set,and the rationality of the calculation model is verified.The numerical simulation results of different flow field structures are compared from multiple angles,including water oxygen concentration and its distribution position,output current and power,and voltage drop.The simulation results show that many geometric parameters(wave height and wavelength,channel width)and intake mode of the new flow field model play a decisive role in PEMFC performance.For the center-inlet four serpentine-wave flow field,in order to solve the phenomenon of low reactant concentration at the end of the channel caused by the long gas diffusion path,the centersymmetric arrangement of the serpentine flow field is innovatively proposed.After verifying the rationality of the model,the geometric variables(wave height and wavelength)are taken as the research object to explore their influence on the output performance of the battery.By analyzing and comparing the results of oxygen concentration distribution,water concentration distribution and pressure drop on the cathode side,it is found that when the wave height is 0.6 mm and the wavelength is 2 mm,the output performance of the proton exchange membrane fuel cell is the best.Compared with the traditional flow field,the output power is increased by 7.6%.The optimized new flow field structure has better oxygen transport and drainage capacity,and produces a more uniform current density.For the edge-inlet four serpentine-wave flow field,the wave height and longitudinal channel width of the flow field are set as key variables.Among them,the channel width is gradient change.After establishing the numerical analytical model,the differences of oxygen concentration distribution,water removal performance,pressure drop and battery output performance of different schemes were compared.The results show that the wave channel design systematically enhances the forced convection between adjacent channels.The increase of normal velocity during gas transmission is beneficial to produce more obvious enhanced mass transfer effect and obtain higher current density in the reaction zone.For the longitudinal channel width,it is found that increasing its size within the effective range can greatly reduce the channel pressure drop without reducing the output power,thereby improving the overall efficiency.When the wave height is 0.6 mm and the longitudinal channel width changes in a gradient manner,PEMFC can obtain the best overall performance.Finally,the edge inlet flow field scheme and the central inlet flow field scheme with good comprehensive performance are processed by external condition control variables including inlet flow rate,computational domain size and rib width ratio,and the influence of inlet mode on battery output performance and reactant concentration distribution is deeply explored.The results show that the central inlet flow field has better fluid distribution characteristics and current density distribution uniformity,which proves that this structure has better effect in improving the output performance of PEMFC.